EXPERIMENTAL

The trait that defines flag sets and operations on them.

Flags are used to provide modifiers for abstract syntax trees that represent definitions via the flags field of scala.reflect.api.Trees#Modifiers. Trees that accept modifiers are:

• scala.reflect.api.Trees#ClassDef. Classes and traits.
• scala.reflect.api.Trees#ModuleDef. Objects.
• scala.reflect.api.Trees#ValDef. Vals, vars, parameters and self-type annotations.
• scala.reflect.api.Trees#DefDef. Methods and constructors.
• scala.reflect.api.Trees#TypeDef. Type aliases, abstract type members and type parameters.

For example, to create a class named C one would write something like:

ClassDef(Modifiers(NoFlags), TypeName("C"), Nil, ...)

Here, the flag set is empty.

To make C private, one would write something like:

ClassDef(Modifiers(PRIVATE), TypeName("C"), Nil, ...)

Flags can also be combined with the vertical bar operator (|). For example, a private final class is written something like:

ClassDef(Modifiers(PRIVATE | FINAL), TypeName("C"), Nil, ...)

The list of all available flags is defined in scala.reflect.api.FlagSets#FlagValues, available via scala.reflect.api.FlagSets#Flag. (Typically one writes a wildcard import for this, e.g. import scala.reflect.runtime.universe.Flag._).

Definition trees are compiled down to symbols, so flags on modifiers of these trees are transformed into flags on the resulting symbols. Unlike trees, symbols don't expose flags, but rather provide isXXX test methods (e.g. isFinal can be used to test finality). These test methods might require an upcast with asTerm, asType or asClass as some flags only make sense for certain kinds of symbols.

Of Note: This part of the Reflection API is being considered as a candidate for redesign. It is quite possible that in future releases of the reflection API, flag sets could be replaced with something else.

For more details about FlagSets and other aspects of Scala reflection, see the Reflection Guide